accessible category and Ind
Proposition
Let be a regular cardinal and an infinity category.
TFAE:
- is a -kappa accessible infinity category.
- where is the full infinity subcategory containing -compact objects, where furthermore is essentially small.
- there exists a set of -compact objects such that for full subcategory containing those objects
- there exists a small infinity category such that
see:
Proof
1) 2)
FW: 6.62
sketch:
The inclusion
induces a factorization
(cf. universal property of Ind kappa)
one can show, that this induced map is an joyal equivalence (todo :/):
- admits a right adjoint
- happens to preserve -filtered colimits consisting of
- the counit (analogously for the unit) are equivalences on
- as generates under filtered colimits, this induces an iso on each object.
- natural equivalence between infinity functors and objectwise isomorphism
2) 3)
Let for some small infinity category .
Note that each object is a retract of some (where is identified with the image, cf. compact object as filtered colimit as retract)
This follows from retracts of a small subcategory as essentially small subcategory
3) 4)
special case